As the use of printers for printing images such as text, graphics, and photos has become widespread, it has become desirable to obtain high quality print output as quickly as possible. One way to obtain faster print output is to print each portion of the print medium using only a single pass. In single pass printing, the print elements and the print medium are moved relative to each other in such a way that the print elements are positioned adjacent a given region of the print medium only once during printing.
To achieve high quality results, it has become common for printing elements to be tightly packed together, with densities of 300, 600, or more print elements per inch. At such densities, it is not uncommon for particular print elements to be, or to become, defective. Defective print elements typically produce visible defects on the printed medium that degrade print quality. Such undesirable defects may include, for example, white or different-colored lines or streaks, which are often more noticeable in regions of uniform color. To compensate, some printers may use multiple pass printing, which minimizes such streaks by overprinting the same region of the print medium with non-defective print elements, but a multiple pass printing mode disadvantageously increases print time and decreases throughput.
Other image-forming devices, such as pixel-addressable displays and digital light processing (DLP) projectors, can also have imaging elements (elements that form a portion of the image) that are defective, and thus exhibit undesirable defects in the quality of the displayed or projected image.
For these and other reasons, there is a need for the present invention.